Temperature is a growing concern in most integrated circuits (ICs). Die temperature should be controlled because temperature impacts the timing, leakage power, package design, and life-time of the IC device. For example, integrated circuits will run slower when they are hot, and their life-time will be reduced exponentially with increasing temperature. Furthermore, leakage power increases exponentially with temperature, which can cause a thermal runaway. The problem is further exacerbated by increasing power densities. As semiconductor technology continues to improve, it is possible to implement circuits in ever higher power density.
Programmable logic devices (PLDs) have by their nature resulted in lower power density at the same process nodes when compared to application specific integrated circuits (ASICs) and microprocessors. However, the recently high performance hard macros, such as a processor core or a power PC (broadly referred to as non-programmable dedicated components) have been embedded in PLDs which have the potential to induce localized heating and hot spots. Furthermore, because the customer design is unknown, it is very difficult to ascertain the temperature gradient at the user selected regions of the design.
One can use an external temperature measuring device, e.g., an external thermocouple, to measure the temperature of the die, but such approach is impractical and inefficient in that external equipment will be needed. Furthermore, there may be variations from die to die, thereby affecting the accuracy as to how temperature is correlated. Additionally, if the IC is a PLD, the temperature gradient can only be ascertained after the design has been implemented by the customer. Finally, once the IC is fielded into a piece of equipment, it is often impractical to monitor the temperature gradient during run time.